The circuit line structure on a circuit board or a display device may have a discontinuous circuit pattern due to different design. And a part of the circuit pattern, such as in the rescue line, the signal line, or the data line, is required to be arranged as “open”. In case of the pattern of the part having open is not consistent with the pattern on the photo mask which is applied to define circuit pattern by a stepper, it is relatively inconvenient to use the photo mask step by step for defining the circuit pattern.
An active type display device is shown below and includes a base plate and a pixel array mounted on the base plate. The pixel array includes a plurality of scan lines and a plurality of data lines transversely crossing the scan lines to define a plurality of pixel units. A TFT (thin film transistor) serves as a switch for each of the pixel units. The TFT generally includes a source and a drain connected to the respective scan and data lines of the respective pixel unit. When the scan or data line is broken at a point, the signal cannot be fed into the pixel unit located beyond the broken point, thereby causing poor display ability of the pixel unit, thus quality deterioration of a displayed image occurs.
FIG. 1 shows a conventional display device 10 which includes a plurality of scan lines 1, a plurality of data lines 2 and a rescue circuit line 7, wherein the data lines 2 vertically and respectively cross the scan lines 1 to define a plurality of pixel units, which form an active area. The rescue circuit line 7 can be divided into a first rescue line portion 7a and a second rescue line portion 7b by the open 6 such that the first rescue line portion 7a surrounds a portion of the active area while the second rescue line portion 7b surrounds the other portion of the active area. As illustrated, the display device 10 has two breaks 3a, 3b. The break 3a is encircled by the first rescue line portion 7a while the break 3b is encircled by the second rescue line portion 7b. Two opposite ends of each break 3a or 3b are connected to the first and second rescue line portions 7a, 7b via the conductive lines 8, respectively, so as to fed signal via the first and second rescue line portions 7a, 7b. 
In the normal condition (i.e. there is no break in the scan line 1), the scan line 1 scans the pixel units from the left terminal 9a to the right terminal 9b. When the scan line 1 has the break 3a, the scan line 1 scans only those pixel units located between the left terminal 9a and the break 3a. At such circumstance, the conductive line 8 can be applied to connect the terminals 9a, 9b and the first rescue line portion 7a in order to feed the signal into the pixel unit located between the right terminal 9b and the break 3a. 
If the first and second rescue line portions 7a, 7b have to be formed on a large size plate, a photo mask with small dimension is usually applied in the lithography by the stepper in order to enhance the performance.